We define the (energy) interpolant \(\mathbf {u}_{I}\in \mathbf {W}_{h}\)  of a sufficiently smooth vector-valued field \(\mathbf {u}\)  as the unique function in \(\mathbf {W}_{h}\)  sharing the same degrees of freedom of \(\mathbf {u}\) .
We have the following local and global interpolation property.
We omit the proof as it would be a fairly standard modification of the analogous results in [1]}.
